Description of the Related Art
Most polycarbonate resin produced at present is bisphenol A type polycarbonate which is produced from 2,2-bis(4-hydroxyphenol)propane (bisphenol A) as a raw material.
The bisphenol A type polycarbonate is a well balanced polycarbonate in terms of cost, heat resistance, mechanical strength, etc. Recently, polycarbonates having superior physical properties have been desired with an expansion of polycarbonate use, and polycarbonates having a variety of structures have been developed.
However, there is a need for the development of polycarbonates having even more superior physical properties or specific physical properties.
For example, a siloxane copolymer polycarbonate which is a modified polycarbonate having improved release properties and flowability has been developed (JP-A-50-29695 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-3-079626, JP-A-5-155999, JP-A-7-258398 and JP-A-7-165897).
Furthermore, polycarbonate resin is often used as a composition containing additives, such as a releasing material or a fire retardant, in order to strengthen release properties, flowability, weather resistance, fire retardancy, etc. Especially, when silicone (diorganopolysiloxane) is used as an additive, abrasion resistance and the release property are improved and fire retardancy is obtained, such that the additive is useful for a polycarbonate resin. However, when diorganopolysiloxane is added in a large amount, there is a problem in that the polycarbonate molded article turns muddy-white, and transparency which is a characteristic feature of polycarbonate is decreased. Particularly, even when the resin is dissolved in a good solvent in which the resin is easily dispersed in a homogeneous manner, the resin liquid can become muddy-white and a wet molded article having a good appearance is not obtained.
On the other hand, a resin composition blended from a siloxane block copolymer polycarbonate and an ordinary polycarbonate with the objective of improving fire retardancy, release properties and flowability has been developed (JP-A-55-1660052, JP-A-62-146953, JP-A-5-140461 and JP-A-1-161048).
The above described modified polycarbonate has an improved release property, water repellency, flowability and abrasion resistance, etc., as compared to conventional polycarbonates. However, there is a need for further improvement in abrasion resistance, and the above modified polycarbonate is not satisfactory.
Furthermore, the above described resin composition blended from a siloxane block copolymer polycarbonate and an ordinary polycarbonate is improved with respect to the above described properties. However, its overall properties are not necessarily satisfactory when a diorganopolysiloxane additive is employed.
Therefore, a polycarbonate having improved compatibility with a diorganopolysiloxane additive and a polycarbonate resin which exhibits no loss in transparency and which retains its abrasion resistance and release property has been desired.
The present inventors conducted extensive research in order to solve the above problems of the prior art. As a result, the present inventors discovered a polycarbonate polymer having a repeating unit having a specific grafted polysiloxane structure, to thereby complete the present invention.